OtherHelp with my server, forum, MySQL - Site unresponsive for the most part

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My hosting (Hostgator) tells me I need to hire somebody who will help me out with MySql etc because the site cannot handle more than 1000 or 1200 people inside, it crash, right now is unresponsive and I am honestly going nuts. They said I need help from somebody who knows about Xenforo. This is one of the last answers from them among many others so you can have an idea of what's going on:

Hello, Thank you for your patience. Reviewing the logs during the time of the mentioned issues, I'm showing numerous PHP-FPM workers were stacked waiting on MySQL responses, which in return caused request delays as there were no available workers. The MySQL queries which were seen stacked at the time, were mainly related to numerous similar queries:

While the related table already has indexes to improve performance, the sheer amount of data which needs to be processed still causes issues as queries stack. As these queries were all for the same thread ID, it's possible tuning your site's cache settings may help avoid recurring issues.

Today the site was doing perfectly and when it reached 1800 people inside it went down with a running time error, after that I'd try to reboot, didn't work, the site is apparently down, no error but on a loop trying to load but it won't land. I will pay for the service as I don't know how to do anything inside the server, I am very honest and straightforward, my site is down as of right now and I am going nuts.